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Emission Tests

EMISSION TEST PROCEDURESA specified vehicle driving or engine operation schedule of varying speeds and loads - represents real life driving/usage pattern of the vehicles and engines. test schedule of vehicle or engine operation is known as driving cycle.Use of emission sampling systems and analyzers that operate on the working principles specified in the emission regulations.The new production vehicles and engines are tested for compliance with the emission standards in a government approved laboratory.Test cycles used in the USA, Europe and Japan for emission measurement and certification of vehicles/engines for compliance with the standards differ and so also the numerical values of the emission limits. Direct comparison between standards in different countries is generally not possible

Units of Emission LimitsTwo types of emission limitsFor the light and medium duty vehicles, passenger cars and, two and three wheelers are in terms of mass of pollutant emitted per unit distance travelledi.e., g/km ( g/mile in the USA , 1 g/km = 1.61 g/mile).For heavy duty vehicles and engines test is carried on the engine itself and the limits are specified in terms of mass of pollutant per unit of work done i.e., g/kW-h or g/bhp-h (1 g/kW-h = 1.34 g/bhp-h) .Test cycle and measurement procedures have been accordingly developed whether test is to be done on a vehicle or on the engine.

Driving Cycles for Light Duty VehiclesEmission test driving cycles are composed of a cold start period, idling, moderate acceleration and deceleration, and cruise modes. Test cycle is given in terms of vehicle speed versus time. Light and medium duty vehicles are driven through the prescribed driving cycle on a chassis roller dynamometer. During operation the engine is required to develop road horse power that depends on the vehicle speed for a given vehicle. The road horsepower requirement versus speed data as provided by the vehicle manufacturer or determined by vehicle coast down test is stored into chassis dynamometer controller to simulate the real life road operation of the vehicle. The vehicle weight i.e. inertia needed during transient modes of the driving cycle is simulated by mechanically changing the rotating masses or electronically changing the inertia on the roller dynamometer.

European Test Driving CycleEuropean test cycle is composed of steady operation modes derived from the actual vehicle operation data on road.Although it consists of acceleration and deceleration modes but as all the modes represent averaged operating conditions, the cycle is often referred to as STEADY MODE CYCLE.It has two parts;Urban driving cycle (ECE 15) andExtra-urban driving cycle (EUDC)

ComparisionECE-15 cycleEUDC Cycle

Distance, km4.0526.955Time, s780400Average speed, km/h1962.5Maximum speed, km/h50120Acceleration, %time21.16-Maximum Acceleration, m/s2-0.833Deceleration, % time13.8-Maximum Deceleration, m/s2--1.389Idle, % time35.4-Steady speed, % time29.3-

Heavy Duty Vehicle EnginesThe first European test procedure for heavy duty vehicles, R-49 used 13-mode test havingFive different load points each at the rated and peak torque speeds Three idling speed points one in the beginning one in the middle and the third at the end. Each mode had a different weighing factor. A new test procedure has been adopted from the year 2000 along with implementation of Euro 3 standards.It consists of two separate tests each of about 30 minutes duration as below;13-mode steady state cycle (ESC) with a dynamic load response (ELR) smoke testA transient test cycle (ETC)

Steady state cycle (ESC) is used to prevent abnormally high emissions if an engine is made to operate at extreme conditions where emission controls may not be very effective.On the other hand, the transient cycle (ETC) represents the actual operating conditions and is better suited for the engines operating on alternative fuels or employing after treatment devices.For certification to Euro 3 standards, the conventional diesel engines are tested by the ESC only.However, the diesel engines with advanced emission control systems such as after-treatment devices and the SI engines such as natural gas engines are tested by both the procedures.

US FTP-75 CycleUS test procedure known as Federal Test Procedure -75 (FTP-75) is a transient cycle consisting of a typical actual driving trace for the light duty vehicles. It consists of four phasesCold transition phase of 505 seconds with a weighting factor of 0.43Stabilized phase of 867 seconds with a weighting factor of 1.0Hot soak phase of 10 minutesHot transition phase; repeat of first phase of 505 seconds with a weighting factor of 0.57

Cycle Details:Length11.09 miles (17.85 km)Max. Speed:56.7 mph (91.2 km/h)Time1372 s + (600 s stop) + 505 s The first 505 s are repeatedafter a 10 minute stop (hotsoak)Idle :17.3 %Av. Speed21.3 mph (34.3 km/h)Steady speed:20.5%Deceleration:26.5%

Total vehicle driving schedule is of 31 minutes. In addition, after operation for 1372 seconds engine is switched off in hot condition to allow hot soaking period of 10minutes. The total distance covered is 11.09 miles. The vehicle is preconditioned before test by soaking it for 12 hours at a temperature between 20 to 30 C. The test begins with cold start. FTP-75 procedure was the first to use CVS (Constant Volume Sampling) method for measurement of the mass of the pollutants emitted per km or mile travelled.The sample of diluted exhaust gas with air from CVS system is collected in three separate bags, one each for the three phases of vehicle operation. The concentration of pollutant in each bag and total volume of diluted exhaust gases for each test phase is determined to calculate the mass of pollutants emitted.Weighting factors corresponding to each phase are used to give mass emission values for the total cycle.

US Heavy Duty Test ProcedureIn the USA until 1984, a steady state test cycle consisting of 13 different engine speed and load combinations was used for measurement of gaseous exhaust emissions from the heavy-duty vehicle engines. Emissions were measured under engine idling, and at rated and maximum torque engine speeds as in European R-49 cycle but at different engine loads Engine operating modes had different weighting factors than the European test procedure.From 1985, a transient mode test replaced the 13-mode test. This test cycle was developed from the driving pattern data measured in New York and Los Angeles. The cycle represents driving pattern only for the city operation

It contains the traffic characteristics of congested urban, uncongested urban and city expressway driving. The US transient cycle test is run over a full range of load and speed conditions with equal weighing factor to each operation point of the cycle. The total test consists of three phases, cold start cycle, hot soak and hotstart cycle; each phase of 20 minutes duration. Data on engine speed, load and gaseous emissions are monitored once per second. Computer controlled engine test bed and data acquisition are used. The emission results are integrated over the test cycle. The weighting factors for the cold start and hot start cycles are 1/7 and 6/7, respectively.

Dynamometer BasicsLOAD deviceIt applies a load to an engine so the performance of the engine under a variety of circumstances (Power, Speed)

Constant Volume Sampler (CVS)When emissions are to be measured from a vehicle being run on a driving cycle, sampling of the representative gas is very critical.Used in European, US and other tests to make it possible that a representative sample of the exhaust gas is withdrawn for measurement of the gaseous emissions.

CVSEntire exhaust gas from the vehicle is diluted with the filtered room air.Air to exhaust gas dilution ratio of about 10:1 is used. Dilution with air lowers partial pressure of unburned hydrocarbons and water, and prevents their condensation in the sampling line.Diluted exhaust gas is drawn by a constant volume pump system employing either a positive displacement pump (PDP) or a critical flow venturi (CFV) and a blower. PDP capacity of about 10 to 12 m3/min of air flow provides sufficient dilution for most passenger carsVolume flow rate of the diluted exhaust (exhaust gas + air) is maintained constant throughout the test .

CVS Before the diluted exhaust gas enters the CFV or PDP, its temperature is controlled within the 5 C of the average gas temperature during the test by a heat exchanger. From the diluted gas a small sample is continuously withdrawn and collected in evacuated Teflon bags. This process integrates the concentration of the pollutants over the entire driving schedule. A small part of the dilution air is sampled simultaneously and collected in a separate bag to correct for any background concentration of pollutant present in the dilution air.

CVSThe sample bags are analyzed after the test is completed. The mass of individual pollutants is determined from its measured concentration in the samplebag, its density and the total volume flow rate of the diluted exhaust during the test through CVS

CVS

Chassis DynamometerA service tool that allows the operator to safely place a controlled load on a vehicle. With the use of a dyno, a vehicles primary power train components, including the engine, transmission, and differential can be analysedVehicle components such as the braking, cooling, and electrical systems, can be properly operated throughout a vehicles power and speed range.Assembly deficiencies may be detected before the vehicle is drivenActual evaluation of an engines operating condition may be performed. The dynamometer is the final quality test before a vehicle is put into service.

ConstructionThe chassis dyno itself is only one component of a complete chassis dynamometer system. A typical dynamometer system consists of a chassis dynamometer and the following components: fuel measurement systemroom exhaust systemdata acquisition and control system.Parts of dynoRoll setAbsorption unitTorque indication system.

Roll SetRoll sets come in a variety of diameters depending on the application. An automotive chassis dynamometer will typically have smaller roll sets, while a largetruck dynowill have a larger set. These dyno roll sets are placed in a specially designed frame and are either coupled directly to the dynamometer absorption unit or to a belt drive system. Dyno roll sets are available in both fixed and adjustable width versions which can accommodate a variety of wheelbases for testing multiple vehicles on a single machine

Absorption UnitA water brake absorber when used in a chassis dynamometer are very similar to an engine dynamometer. In addition to water brake absorbers, chassis dynos can also be equipped with eddy current and AC regenerative absorption units.An eddy current absorber uses electrical current to produce a load. Eddy current dynamometers require an electrically conductive core, shaft or disc, moving across a magnetic field to produce resistance to movement. Available in both air cooled and liquid cooled applications, eddy current chassis dynamometers provide quick response rates. Most eddy current absorbers use cast iron discs, similar to vehicle disc brake rotors, and use variable electromagnets to change the magnetic field strength to control the amount of braking.

Torque indication systemAbsorption unit is restrained using a torque arm that is connected to a load cell. The load cell measures the force with which the stators are trying to rotate. By knowing the distance from the axis of the absorber to the torque arm, torque can be measured by:Torque = force x distanceHP = (torque x rpm)/5252

WorkingA vehicle or chassis is driven onto a chassis dynamometer and the vehicle is secured using straps or chains typically provided with the dynamometer system. The vehicle then performs a series of tests that mimic the operating conditions the vehicle would face during its intended use. These tests can be performed by an operator either inside or outside of the vehicle, or through an automated test depending on the control system supplied with the chassis dyno.

Coast-down test procedureCoast-down test procedure necessary to set chassis dynamometer road load to reflect actual vehicle characteristicsAerodynamic dragTire rolling resistanceWheel bearing and brake dragAxle and transmission spin lossInertia of drivetrain elements

Vehicles removed from impound according to schedule likely two vehicles tested at onceVehicles, driver weighed; vehicles instrumentedVehicles driven to 70 MPH on lowest lane of oval trackTransition to track apron on straight; shift to neutralCoast down from 70 to 10 MPHRecord data; use to derive Polynomial Force Coefficient from velocity, time and massVehicles returned to impound